<div class="panel panel-primary">
  <div class="panel-heading">第一种：父子组件之间通讯</div>
  <div class="panel-body">
      <test-child #child (follow)="doSomething()" childpaneltitle="一个新的标题"></test-child>
      <button (click)="child.childFn()" class="btn btn-success">调用子组件方法</button>
  </div>
</div>
